Tripod constant velocity joints, such as joints of the “GI” type sold by GKN Driveline S.A., typically include a male element having at least two trunions and a shaft extending along a first axis and having an outside diameter (DAE). Each of the trunions is provided with a rolling surface which extends along a respective second axis, in particular an axis perpendicular to the first axis, and which has a rolling surface diameter (DSR). For each trunion, a wheel mounted on the trunion rotates about the second axis, and is free to slide along said axis. The wheel has an outside diameter (DGE). A female element comprises, for each wheel, a pair of paths and defines a primary circle path.
U.S. Publication No. 2002/0032063 A1 describes a constant velocity joint of the foregoing type having dimensional proportions with specific ratios for the purpose of reducing the size or bulk of the joint while obtaining equilibrium between its structural strength and its service life.
The structural strength of a joint relates to the mechanical strengths of the elements making up the joint when subjected to static and dynamic stresses. The service life of the joint relates to the ability of the contact surfaces of the paths, the wheels, and the needles to withstand wear, such as scaling.
According to U.S. Publication No. 2002/0032063 A1, the parameters that have an influence on structural strength are, amongst others, shaft diameter (ds), trunion diameter, wheel wall thickness, and wheel width. The parameters that have an influence on service life are the diameter (PCD) of the primary circle of the guide paths, trunion diameter, needle length, and needle diameter.
The joint of U.S. Publication No. 2002/0032063 A1 has a ratio of shaft diameter (ds) over path primary circle diameter (PCD) that lies in the range 0.5 to 0.55. The ratio of wheel width over wheel outside diameter is equal to or less than 0.32, and preferably lies in the range 0.27 to 0.24. The ratio of trunion diameter over wheel diameter lies in the range 0.54 to 0.57.
Automotive applications for such joints demand at least equivalent service life in still more compact packages.